Some naphthyridine and quinoline derivatives of ampicillin possessing antibacterial activity are disclosed in U.S. Pat. No. 3,951,955. They are, however, not of sufficiently low toxicity.
The present inventors have found that pyrazinoquinoline derivatives of penicillins of the formula (I) described hereinafter have excellent anti-pseudomonas activity and other antibacterial activity against gram-positive and gram-negative bacteria, and are of extremely lower toxicity as compared with the known penicillin derivatives.